The production of high purity carbon nanostructures such as single wall and multi wall nanotubes and nanofibers as well as nanomaterials from other elements has been achieved by several methods, including arc discharge, pulsed laser vaporization (hereinafter “PLV”), and chemical catalytic vapor deposition (hereinafter “CCVD”). To date one promising technology for producing nanostructures is CCVD. A CCVD nanostructure reactor enables the control of most of the physical and chemical parameters that influence both the nucleation and the growth of highly pure carbon nanostructures. The important parameters for producing nanostructures include the nature and support of a catalyst, a hydrocarbon source and concentration, a flow rate and type of carrier gas, a reaction time, a reaction temperature and thermal stability in a reaction zone of a nanostructure reactor. Additionally, in order to efficiently mass-produce highly pure nanostructures at low cost, energy consumption during the heating process need to be minimized.
One of the major limitations of a conventional CCVD nanostructure reactor for nanostructure synthesis is the size of a susceptor that can be used. Large size susceptors, desirable for producing large quantities of carbon nanostructures, introduce difficulties in controlling the hydrocarbon gas flow over the catalyst powder bed and attaining tight control of a reaction temperature. Furthermore, the use of conventional ovens results in temperature gradient along the length of the oven. This temperature gradient results in varying temperature conditions that have a significant negative impact on the quality, characteristics, and purity of carbon nanostructures grown therein. Additionally, conventional ovens consume large amounts of energy and heat inefficiently.
An alternative technology for heating a reaction zone of a nanostructure reactor is inductive heating (hereinafter “IH”). IH can be easily controlled, can be focused on catalyst particles alone, and presents a uniform temperature within the reaction zone. IH also consumes significantly lower energy compared to classical heating because it mostly heats the reactants and their physical support such as a susceptor. Another advantage of IH is the time required for the catalyst particles and “susceptor” to reach the temperature of reaction is about 2 to 3 minutes, which is much shorter, compared to the about 30 minutes required for classical heating. Altogether, the time required to produce a batch of nanostructures by IH is approximately one third of the time required by using a classical oven to produce a similar batch of nanostructures.
In an IH nanostructure reactor, high purity graphite is typically formed into the shape of a boat and used as the susceptor. The susceptor boat lies within the radio frequency (hereinafter “RF”) field, absorbs its energy, and heats the catalyst and other reactants. If the RF field intensity is increased, the susceptor temperature rises. Therefore, the amount of RF energy has to be carefully controlled, particularly if there are variations in power or ambient temperature. Additionally, there is the aforementioned 2 to 3 minutes of susceptor warm-up time to achieve temperature equilibrium. The length of this warm up time period and the corresponding cool down time period upon reaction completion is a function of the thermal mass of the susceptor. Susceptor mass becomes an increasingly important synthesis bottleneck as one attempts to scale up for large scale production.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.